The advent of various communication systems and increasing deployment of sophisticated applications in mobile end systems, has stressed existing resources like frequencies available to facilitate these communications. Different multiple access technologies have been proposed to support the increasing traffic within communication networks. Frequency Division Multiple Access (FDMA) is one such technology that allows communications by assigning and reusing frequencies between different users. Another example of multiple access technology is Code Division Multiple Access (CDMA) which employs spread spectrum technique to simultaneously accommodate different users on a broad spectrum.
Accordingly, CDMA systems are characterized by bursty communications wherein the communication channels are populated during data transmission but remain silent at other times. This is rectified by a flexible use of channels wherein channels are assigned for different tasks based on necessity. Thus, channels are connected for a user only during data transmissions, reassigned for other tasks during the period when there is no data transmitted and are reconnected again upon data transmission.
Channels in a communication system may be divided into physical and logical channels wherein physical channels are the frequencies carrying communications and logical channels are schematic partitions created on these frequencies based on the tasks to be performed. A single physical channel may hence be divided into one or more logical channels. In other words, logical channels are different names assigned to the physical frequencies based on the tasks involved.
Physical channels are normally further divided into dedicated channels and common channels depending on the entities being serviced. A dedicated channel is assigned to facilitating communications between a base station and a specific user. A common channel is shared by different users and is used by a base station to transmit signals that are commonly communicated to all users within the geographic area (cell) being serviced by the base station. Examples of dedicated channels include fundamental channel (FCH), a dedicated control channel (DCCH), as well as a supplemental channel (SCH). The FCH can transmit a voice signal, a data signal, and a signaling signal or a control signal. The DCCH transmits data signals as well as control signals, in a discontinuous transmission mode wherein data transmission occurs only if transmission data is generated from a higher layer, which makes the DCCH suitable as a control channel for providing packet service efficiently. The SCH is a channel that is optionally used when large amount of data needs to be transmitted. Examples of common channels on a base station-to-mobile forward/down link include paging channel, broadcast channel, and forward common control channel to name a few. An access channel, an enhanced access channel, and a reverse common control channel are some of the common channels on the reverse link.
Logical channels established on the dedicated physical channels include a dedicated signaling channel (DSCH) and a dedicated traffic channel (DTCH). The DSCH can be assigned on the FCH and the DCCH to exchange control signals between a base station and a mobile station, whereas the DTCH can be established on the FCH, DCCH, and SCH to exchange user data. Common logical channels assigned on the common physical channels include a common assignment channel used by a base station to acknowledge a user/mobile terminal, a common control channel (CSCH) for transmitting a control signal and a common traffic channel (CTCH) for transmitting user data. The common logical channels can be established on the forward link as well as the reverse link.
When data is generated for transmission by a user, a service request is transmitted via established communication channels and based on the negotiated service options/availability resources are assigned to the user. Accordingly, various control and data resources are assigned on common/dedicated channels. For example, supplemental resources may be assigned subject to availability if it is anticipated that large amount of data will be transmitted and if the service options associated with the user permit assignment of such supplemental resources. A resource assignment message detailing the various resources including information regarding supplemental resources allotted is communicated by the base station to the user upon allocation of the resources. Hence, when the user communicates data, the data is demodulated based on the resources assigned.
Due to various reasons such as limited range and deleterious effects such as Doppler shift in moving terminals, the resource assignment message from the base station may be erased. This leads to a situation where the user is unable to demodulate messages since it is not know what, if any, resources have been assigned for that particular communication session. For example, if the service options permit allocation of supplemental resources, erasure of the resource assignment message will prevent the user from knowing if any supplemental resources have been assigned. Additionally, availability of supplemental resources can lead to non-optimal repetition of coded bits.